Metformin Treatment on Cognitive Impairment of Schizophrenia Co-morbid Metabolic Syndrome

In this study, the investigators will investigate the impact and the related mechanism of metformin treatment on cognitive impairment of schizophrenia with a high risk of metabolic syndrome. Patients will be randomized to the metformin group or non-metformin control group (40 patients per arm) . Clinical assessment will be done at screen/baseline, 4 week, 12 week and 24 week. The specific aims are to compare the metformin group versus controls on: 1) clinical core symptoms; 2) cognition. Biological samples also will be collected, and stored to research related mechanisms. Clinical symptoms will be measured by the Positive and Negative Syndrome Scale and Calgary Depression Scale for Schizophrenia (Chinese version). Cognitive function will be assessed by the MATRICS Consensus Cognitive Battery. The investigators hypothesize that 1) metformin may improve the cognitive impairment of schizophrenia patients; 2) metformin may alter oxidative stress indexes or inflammatory biomarkers thus influencing the oxidative and inflammatory mechanism, and the structure and function of the hippocampus that may be significantly associated with cognitive function.